What is a Faraday Cup?
 

    A Faraday Cup is device for measuring the current in a beam of charged particles. In its simplest form it consists of a conducting metallic chamber or cup, which intercepts a particle beam. An electrical lead is attached which conducts the current to a measuring instrument. Detection can be as simple as an ammeter in the conducting lead to ground or a voltmeter or oscilloscope displaying the voltage developed across a resistor from the conducting lead to ground. A bias voltage applied either to the cup itself or a repelling grid preceding the cup, or a magnetic field,  is usually used to prevent secondary emission from distorting the reading. The design can be significantly more complicated when it is necessary to make measurements of very short pulses or very high energy beams which may not be fully stopped in the thickness of the detector. Some examples can be found at the following sites:


http://en.wikipedia.org/wiki/Faraday_cup

http://www.casetechnology.com/implanter/faraday.html


    The name of the device is intended to honor Michael Faraday (1791-1867), the discoverer of electro-magnetic induction, electro-magnetic rotations, the magneto-optical effect, diamagnetism, field theory.